Problem: Solve for $y$ : $8 + y = -7$
Solution: Subtract $8$ from both sides: $ \begin{eqnarray} \\ 8 + y &=& -7 \\ \\ {-8} && {-8} \end{eqnarray} $ $ \begin{eqnarray} \hphantom{8 + y} &\hphantom{=}& \hphantom{-7} \\ y &=& -7 {- 8} \\ \end{eqnarray} $ Simplify. $ y = -15$